karldub

I'm doing a 700c to 650b conversion and planning to get some fenders. Honjo makes fenders for both 650b and 700 wheels, but I have a hard time finding the ones I want in the size of 650b.

I'm going with 650 x 38 tires. Anyhow, since my frame is originally built for 700c, I'm thinking the 700-fenders should work with the bike frame as well - and there should be no danger in getting som extra clearance, right?

Does anybody have experience with this or any thoughts on pro's and cons with going with the 700 version?

scarlson 

@southpawboston has used 700c fenders on a 650b wheel. He re-radiused them, as I recall.

I have done a number of 650b conversions in recent years and they look fairly ridiculous with 700c fenders on. Like there will be quite a bit of room between the fender and the tire in a few places unless you re-radius them. You can carefully do a re-radius by bending them by hand, but you must take great care not to kink the aluminum.

southpawboston

Yep, pretty easy to re-radius most metal fenders (SS Berthouds maybe not so easy). Here's a photos of a set of VO 700C Zeppelins with one re-radiused to 650B:

southpawboston

And here's a multi-part blog series I did on metal fender installation, which goes over, among other things, how to successfully re-radius a fender.

HeikoS69

Factory fender radius for 650b: 355 mm
Factory fender radius for 700c: 358 mm
Difference 3 mm.
I had a pair of factory H47s labeled 650b. After careful measurement, I found that the radius was 358 mm (i.e. for 700c). The label had been overstickered.

Wharf Rat

southpawboston Ive used your blog post multiple times when mounting fenders. It’s phenomenal, thank you. I’ve changed the radius of multiple sets of fenders and it’s easy.

USAZorro

If the frame was designed for 700c wheels and you're using the same attachment points, there's ZERO reason to change the radius. You'll end up with a couple more mm clearance than you would with 700c wheels, but that's not an issue.

scarlson 

Maybe it'd be fine for some frames, but not any of the frames I have worked with. I went through a phase where I was using all 700c wheels, and now I am switching to 650b wheels on the same frames, and they universally require different fender setups to avoid huge gaps. Granted, these are '70s "sport touring" frames with lots of tire clearance, and were set up with 700x38 tires and fenders. Change to 650x42 or even 48 and you are going to have a completely different fender placement. To use just one example, if the frame has horizontal dropouts, it will have a lot of space in front of the back wheel in order to get it out by sliding it forward without deflating the tire. So you mount the fender directly to the chainstay bridge so you can get the wheel out. If you change to 650b and your wheels will have 10-20mm smaller radius, so you will need to mount the fender closer to the tire to have decent coverage. And you can, because the wheel will not come so far forward to remove it. So you will end up with 10-20mm of spacers in there, and definitely some massaging will be necessary to make the fender fit. I have a situation like this on my Colin Laing tandem right now, which I can photograph after work if I think of it. The fenderline looks ridiculous. Like a motocross bike or something.

USAZorro

On the front, nothing changes positionally, and if anything, a 700c fender will give better coverage.

The math on the clearance is 622 - 584 = 38 / 2 = 19 mm difference, but then add back 4-10 mm for the larger tire, so 9 - 15 mm. With the "right" 700c fender, you still get a generous, but reasonable clearance. However, if you use a 650B fender on the rear on a frame with fender attachments intended for 700c using the same attachment points, you will naturally end up with a much larger gap at the front than the rear if you position the axle at the same place. It's the 650B fender that you will need to monkey with in this scenario if you wish to have an acceptable fender line.

This is what happens on a 70's sport tourer converted to 650B when you use 650B fenders without compensating. Note that the front is just fine. This would be closer to even if I were to pull the rear wheel forward a bit and/or add a spacer behind the mount between the rear chain stays, but in retrospect, I think this would have come out slightly nicer had I gone with 700c fenders.

Bogester 

Here’s my old Bleriot with 650x38s and my Saluki with 650x42 using 700c fenders. I might have bent them a little with my hands but not much. My old rock combo had 26” wheels and I also used 700c for that….loads of clearance and didn’t look too bad.

southpawboston

Thanks! I needed something to do during COVID lockdown!

rgvg

Quick related question. If you have a threaded boss under the fork crown, and have a small rack mounted (nitto) where it goes through the fork, how do you mount the front fender at the crown? It seems to me like I can't use the boss because I can't thread anything in very far because the rack is in the way. Am I stuck with using an L bracket for the front?

I think there is a boss on the rack as well, so should I just try that instead?